543. 二叉树的直径 Diameter of Binary Tree

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left;
 *     public TreeNode right;
 *     public TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
	public int DiameterOfBinaryTree(TreeNode root) {
		if (root == null)
			return 0;

		/* get the height of left and right sub trees */
		int lheight = height(root.left);
		int rheight = height(root.right);

		/* get the diameter of left and right subtrees */
		int ldiameter = DiameterOfBinaryTree(root.left);
		int rdiameter = DiameterOfBinaryTree(root.right);

		/* Return max of following three
		 1) Diameter of left subtree
		 2) Diameter of right subtree
		 3) Height of left subtree + height of right subtree + 1 */
		return Math.Max(lheight + rheight, Math.Max(ldiameter, rdiameter));
	}

	/*The function Compute the "height" of a tree. Height is the
	  number f nodes along the longest path from the root node
	  down to the farthest leaf node.*/
	public int height(TreeNode node) {
		if (node == null)
			return 0;

		/* If tree is not empty then height = 1 + max of left
		   height and right heights */
		return (1 + Math.Max(height(node.left), height(node.right)));
	}
}

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